In this article we describe 77 arctic fox Alopex lagopus dens in Vindelfjällen, northern Sweden, with regard to distribution, morphology and fox use. The density of dens in the area was 1/21 km2 and dens were more spaced than random. The dens were situated at a mean altitude (± SD) of 915 m a.s.l. ± 74, were on average 3.5 km ± 1.88 from the nearest tree line, had a mean number of 44 den openings ± 32 and a mean area of 277 m2 ± 237. During the 21-year study period, 31 dens were used by arctic foxes and 10 by red foxes Vulpes vulpes. Number of den openings, den area, altitude and distance to the nearest tree line explained 36% of arctic fox den use (P < 0.001) and 21% of red fox use of arctic fox dens during the study period (P = 0.01). Arctic foxes used dens at higher altitude (P = 0.03) and further away from forest than did red foxes (P = 0.03), and tended to breed in dens with more openings (P = 0.08). Arctic foxes used some breeding dens more frequently than others (P = 0.002). Among the breeding dens, both den use and litter size were positively related to den area (den use: P = 0.04; litter size: P < 0.001). Successful arctic fox breeding dens in Sweden thus appear to be characterised by large size and many openings, and they are situated far away from forest at relatively high altitudes.